AnyAccumulator.scala

/*
 * Scala (https://www.scala-lang.org)
 *
 * Copyright EPFL and Lightbend, Inc.
 *
 * Licensed under Apache License 2.0
 * (http://www.apache.org/licenses/LICENSE-2.0).
 *
 * See the NOTICE file distributed with this work for
 * additional information regarding copyright ownership.
 */

package scala.jdk

import java.io.{ObjectInputStream, ObjectOutputStream}
import java.util.Spliterator
import java.util.function.Consumer

import scala.collection.Stepper.EfficientSplit
import scala.collection.{AnyStepper, Factory, IterableFactoryDefaults, SeqFactory, Stepper, StepperShape, mutable}
import scala.reflect.ClassTag

/** An Accumulator for arbitrary element types, see [[Accumulator]]. */
final class AnyAccumulator[A]
  extends Accumulator[A, AnyAccumulator, AnyAccumulator[A]]
    with mutable.SeqOps[A, AnyAccumulator, AnyAccumulator[A]]
    with IterableFactoryDefaults[A, AnyAccumulator]
    with Serializable {
  private[jdk] var current: Array[AnyRef] = AnyAccumulator.emptyAnyRefArray
  private[jdk] var history: Array[Array[AnyRef]] = AnyAccumulator.emptyAnyRefArrayArray
  private[jdk] var cumul: Array[Long] = AnyAccumulator.emptyLongArray

  private[jdk] def cumulative(i: Int): Long = cumul(i)

  override protected[this] def className: String = "AnyAccumulator"

  def efficientStepper[S <: Stepper[_]](implicit shape: StepperShape[A, S]): S with EfficientSplit =
    shape.parUnbox(new AnyAccumulatorStepper[A](this.asInstanceOf[AnyAccumulator[A]]))

  private def expand(): Unit = {
    if (index > 0) {
      if (hIndex >= history.length) hExpand()
      history(hIndex) = current
      cumul(hIndex) = (if (hIndex > 0) cumulative(hIndex-1) else 0) + index
      hIndex += 1
    }
    current = new Array[AnyRef](nextBlockSize)
    index = 0
  }

  private def hExpand(): Unit = {
    if (hIndex == 0) {
      history = new Array[Array[AnyRef]](4)
      cumul = new Array[Long](4)
    }
    else {
      history = java.util.Arrays.copyOf(history, history.length << 1)
      cumul = java.util.Arrays.copyOf(cumul, cumul.length << 1)
    }
  }

  /** Appends an element to this `AnyAccumulator`. */
  def addOne(a: A): this.type = {
    totalSize += 1
    if (index >= current.length) expand()
    current(index) = a.asInstanceOf[AnyRef]
    index += 1
    this
  }

  /** Result collection consisting of all elements appended so far. */
  override def result(): AnyAccumulator[A] = this

  /** Removes all elements from `that` and appends them to this `AnyAccumulator`. */
  def drain[A1 <: A](that: AnyAccumulator[A1]): Unit = {
    var h = 0
    var prev = 0L
    var more = true
    while (more && h < that.hIndex) {
      val n = (that.cumulative(h) - prev).toInt
      if (current.length - index >= n) {
        System.arraycopy(that.history(h), 0, current, index, n)
        prev = that.cumulative(h)
        index += n
        h += 1
      }
      else more = false
    }
    if (h >= that.hIndex && current.length - index >= that.index) {
      if (that.index > 0) System.arraycopy(that.current, 0, current, index, that.index)
      index += that.index
    }
    else {
      val slots = (if (index > 0) 1 else 0) + that.hIndex - h
      if (hIndex + slots > history.length) {
        val n = math.max(4, 1 << (32 - java.lang.Integer.numberOfLeadingZeros(1 + hIndex + slots)))
        history = java.util.Arrays.copyOf(history, n)
        cumul = java.util.Arrays.copyOf(cumul, n)
      }
      var pv = if (hIndex > 0) cumulative(hIndex-1) else 0L
      if (index > 0) {
        pv += index
        cumul(hIndex) = pv
        history(hIndex) = if (index < (current.length >>> 3) && current.length > 32) java.util.Arrays.copyOf(current, index) else current
        hIndex += 1
      }
      while (h < that.hIndex) {
        pv += that.cumulative(h) - prev
        prev = that.cumulative(h)
        cumul(hIndex) = pv
        history(hIndex) = that.history(h)
        h += 1
        hIndex += 1
      }
      index = that.index
      current = that.current
    }
    totalSize += that.totalSize
    that.clear()
  }

  override def clear(): Unit = {
    super.clear()
    current = AnyAccumulator.emptyAnyRefArray
    history = AnyAccumulator.emptyAnyRefArrayArray
    cumul  = AnyAccumulator.emptyLongArray
  }

  /** Retrieves the `ix`th element. */
  def apply(ix: Long): A = {
    if (totalSize - ix <= index || hIndex == 0) current((ix - (totalSize - index)).toInt).asInstanceOf[A]
    else {
      val w = seekSlot(ix)
      history((w >>> 32).toInt)((w & 0xFFFFFFFFL).toInt).asInstanceOf[A]
    }
  }

  /** Retrieves the `ix`th element, using an `Int` index. */
  def apply(i: Int): A = apply(i.toLong)

  def update(idx: Long, elem: A): Unit = {
    if (totalSize - idx <= index || hIndex == 0) current((idx - (totalSize - index)).toInt) = elem.asInstanceOf[AnyRef]
    else {
      val w = seekSlot(idx)
      history((w >>> 32).toInt)((w & 0xFFFFFFFFL).toInt) = elem.asInstanceOf[AnyRef]
    }
  }

  def update(idx: Int, elem: A): Unit = update(idx.toLong, elem)

  /** Returns an `Iterator` over the contents of this `AnyAccumulator`. */
  def iterator: Iterator[A] = stepper.iterator

  def countLong(p: A => Boolean): Long = {
    var r = 0L
    val s = stepper
    while (s.hasStep)
      if (p(s.nextStep())) r += 1
    r
  }

  /** Copy the elements in this `AnyAccumulator` into an `Array` */
  override def toArray[B >: A : ClassTag]: Array[B] = {
    if (totalSize > Int.MaxValue) throw new IllegalArgumentException("Too many elements accumulated for an array: "+totalSize.toString)
    val a = new Array[B](totalSize.toInt)
    var j = 0
    var h = 0
    var pv = 0L
    while (h < hIndex) {
      val x = history(h)
      val n = cumulative(h) - pv
      pv = cumulative(h)
      var i = 0
      while (i < n) {
        a(j) = x(i).asInstanceOf[B]
        i += 1
        j += 1
      }
      h += 1
    }
    var i = 0
    while (i < index) {
      a(j) = current(i).asInstanceOf[B]
      i += 1
      j += 1
    }
    a
  }

  /** Copies the elements in this `AnyAccumulator` to a `List` */
  override def toList: List[A] = {
    var ans: List[A] = Nil
    var i = index - 1
    while (i >= 0) {
      ans = current(i).asInstanceOf[A] :: ans
      i -= 1
    }
    var h = hIndex - 1
    while (h >= 0) {
      val a = history(h)
      i = (cumulative(h) - (if (h == 0) 0L else cumulative(h-1))).toInt - 1
      while (i >= 0) {
        ans = a(i).asInstanceOf[A] :: ans
        i -= 1
      }
      h -= 1
    }
    ans
  }

  /**
   * Copy the elements in this `AnyAccumulator` to a specified collection. Example use:
   * `acc.to(Vector)`.
   */
  override def to[C1](factory: Factory[A, C1]): C1 = {
    if (totalSize > Int.MaxValue) throw new IllegalArgumentException("Too many elements accumulated for a Scala collection: "+totalSize.toString)
    factory.fromSpecific(iterator)
  }

  override def iterableFactory: SeqFactory[AnyAccumulator] = AnyAccumulator

  private def writeReplace(): AnyRef = new AnyAccumulator.SerializationProxy(this)
}

object AnyAccumulator extends collection.SeqFactory[AnyAccumulator] {
  private val emptyAnyRefArray = new Array[AnyRef](0)
  private val emptyAnyRefArrayArray = new Array[Array[AnyRef]](0)
  private val emptyLongArray = new Array[Long](0)

  import java.util.{function => jf}

  /** A `Supplier` of `AnyAccumulator`s, suitable for use with `java.util.stream.Stream`'s `collect` method. */
  def supplier[A]: jf.Supplier[AnyAccumulator[A]] = () => new AnyAccumulator[A]

  /** A `BiConsumer` that adds an element to an `AnyAccumulator`, suitable for use with `java.util.stream.Stream`'s `collect` method. */
  def adder[A]: jf.BiConsumer[AnyAccumulator[A], A] = (ac: AnyAccumulator[A], a: A) => ac addOne a

  /** A `BiConsumer` that adds an `Int` to an `AnyAccumulator`, suitable for use with `java.util.stream.Stream`'s `collect` method. */
  def unboxedIntAdder: jf.ObjIntConsumer[AnyAccumulator[Int]] = (ac: AnyAccumulator[Int], a: Int) => ac addOne a

  /** A `BiConsumer` that adds a `Long` to an `AnyAccumulator`, suitable for use with `java.util.stream.Stream`'s `collect` method. */
  def unboxedLongAdder: jf.ObjLongConsumer[AnyAccumulator[Long]] = (ac: AnyAccumulator[Long], a: Long) => ac addOne a

  /** A `BiConsumer` that adds a `Double` to an `AnyAccumulator`, suitable for use with `java.util.stream.Stream`'s `collect` method. */
  def unboxedDoubleAdder: jf.ObjDoubleConsumer[AnyAccumulator[Double]] = (ac: AnyAccumulator[Double], a: Double) => ac addOne a

  /** A `BiConsumer` that merges `AnyAccumulator`s, suitable for use with `java.util.stream.Stream`'s `collect` method. */
  def merger[A]: jf.BiConsumer[AnyAccumulator[A], AnyAccumulator[A]] = (a1: AnyAccumulator[A], a2: AnyAccumulator[A]) => a1 drain a2

  def from[A](source: IterableOnce[A]): AnyAccumulator[A] = source match {
    case acc: AnyAccumulator[A] => acc
    case _ => new AnyAccumulator[A].addAll(source)
  }

  def empty[A]: AnyAccumulator[A] = new AnyAccumulator[A]

  def newBuilder[A]: mutable.Builder[A, AnyAccumulator[A]] = new AnyAccumulator[A]

  class SerializationProxy[A](@transient private val acc: AnyAccumulator[A]) extends Serializable {
    @transient private var result: AnyAccumulator[AnyRef] = _

    private def writeObject(out: ObjectOutputStream): Unit = {
      out.defaultWriteObject()
      val size = acc.sizeLong
      out.writeLong(size)
      val st = acc.stepper
      while (st.hasStep)
        out.writeObject(st.nextStep())
    }

    private def readObject(in: ObjectInputStream): Unit = {
      in.defaultReadObject()
      val res = new AnyAccumulator[AnyRef]()
      var elems = in.readLong()
      while (elems > 0) {
        res += in.readObject()
        elems -= 1L
      }
      result = res
    }

    private def readResolve(): AnyRef = result
  }
}

private[jdk] class AnyAccumulatorStepper[A](private[this] val acc: AnyAccumulator[A]) extends AnyStepper[A] with EfficientSplit {
  import java.util.Spliterator._

  private var h: Int = 0
  private var i: Int = 0
  private var a: Array[AnyRef] = if (acc.hIndex > 0) acc.history(0) else acc.current
  private var n: Long = if (acc.hIndex > 0) acc.cumulative(0) else acc.index
  private var N: Long = acc.totalSize

  private def duplicateSelf(limit: Long): AnyAccumulatorStepper[A] = {
    val ans = new AnyAccumulatorStepper(acc)
    ans.h = h
    ans.i = i
    ans.a = a
    ans.n = n
    ans.N = limit
    ans
  }

  private def loadMore(): Unit = {
    h += 1
    if (h < acc.hIndex) { a = acc.history(h); n = acc.cumulative(h) - acc.cumulative(h-1) }
    else { a = acc.current; n = acc.index }
    i = 0
  }

  def characteristics: Int = ORDERED | SIZED | SUBSIZED

  def estimateSize: Long = N

  def hasStep: Boolean = N > 0

  def nextStep(): A =
    if (N <= 0) throw new NoSuchElementException("Next in empty Stepper")
    else {
      if (i >= n) loadMore()
      val ans = a(i).asInstanceOf[A]
      i += 1
      N -= 1
      ans
    }

  def trySplit(): AnyStepper[A] =
    if (N <= 1) null
    else {
      val half = N >> 1
      val M = (if (h <= 0) 0L else acc.cumulative(h-1)) + i
      val R = M + half
      val ans = duplicateSelf(half)
      if (h < acc.hIndex) {
        val w = acc.seekSlot(R)
        h = (w >>> 32).toInt
        if (h < acc.hIndex) {
          a = acc.history(h)
          n = acc.cumulative(h) - (if (h > 0) acc.cumulative(h-1) else 0)
        }
        else {
          a = acc.current
          n = acc.index
        }
        i = (w & 0xFFFFFFFFL).toInt
      }
      else i += half.toInt
      N -= half
      ans
    }

  override def spliterator[B >: A]: Spliterator[B] = new AnyStepper.AnyStepperSpliterator[B](this) {
    // Overridden for efficiency
    override def tryAdvance(c: Consumer[_ >: B]): Boolean = {
      if (N <= 0) false
      else {
        if (i >= n) loadMore()
        c.accept(a(i).asInstanceOf[B])
        i += 1
        N -= 1
        true
      }
    }

    // Overridden for efficiency
    override def forEachRemaining(f: java.util.function.Consumer[_ >: B]): Unit = {
      while (N > 0) {
        if (i >= n) loadMore()
        val i0 = i
        if ((n-i) > N) n = i + N.toInt
        while (i < n) {
          f.accept(a(i).asInstanceOf[B])
          i += 1
        }
        N -= (n - i0)
      }
    }
  }
}